1. Field of the Invention
This invention relates in general to an oil and gas well pump, and in particular to a retrievable well pump employing a reciprocating column of liquid to operate the downhole pump.
2. Description of the Prior Art
Once a hole has been drilled from the earth's surface to an oil or gas bearing formation, the oil or gas either flows to the surface naturally or it does not. Natural flow will occur only if the pressure in the reservoir is great enough to overcome the pull of gravity upon the column of fluid in the well.
If the well does not flow naturally, artificial lift must be employed to force the fluid to the surface. Various pumping systems have been applied to this task, including the popular and well known sucker rod pump. Electrical and hydraulic downhole pumps have also been used.
U.S. Pat. No. 2,266,094 (Tebbetts, Jr.), issued on Dec. 16, 1941, shows a hydraulic downhole pump, having telescoping inner and outer barrels. Hydraulic fluid is pumped down the annulus, between the tubing string and the casing, to move the outer barrel up and down. This action pumps the production fluid up the tubing string.